I love the model 57 and the 4 inch guns in particular. I use a load of 7.5 grains of Unique and a 220 grain cast SWC.
Here is a first year gun shipped in December 1964.
Here is one I shoot regularly, shipped in December 1966.
Here is another shooter, shipped in March 1968.
Here is a picture of the 1964 gun on the bottom and the 1966 gun on the top.